The invention relates to a method for controlling cable winding and unwinding in an electrically driven vehicle, in which method a cable is wound by rotating a cable reel by means of a hydraulic motor coupled thereto, and the cable is unwound from the reel in a braked condition by using the hydraulic motor as a hydraulic pump, such that winding and unwinding, respectively, take place in the direction of motion of the vehicle.
Further, the invention relates to an arrangement for cable winding and unwinding in an electrically driven vehicle, the arrangement comprising a cable reel, a hydraulic motor for rotating the cable reel during cable winding and for braking its rotation during cable unwinding, a hydraulic pump for feeding hydraulic fluid and control valves for controlling the feed of hydraulic fluid to the hydraulic motor during winding and for throttling the flow of hydraulic fluid during cable unwinding.
In electrically driven vehicles, such as mine loaders etc., winding and unwinding a cable extending from a reel to a power source are currently regulated either by measuring cable tension, or on the basis of cable reel movements, by means of mechanical information. A problem with this technique is that when trying to control cable winding or unwinding by means of cable tension, the control system is always late, because it does not react until the cable has tightened or slackened. Moreover, turning at bends, for instance, results in that the cable is dragged along the floor, since the system does not wind or unwind cable because a transverse movement does not tighten or slacken the cable in the same way as driving straight forward. Slow control also leads to a situation where the cable may be subjected to unexpected, sudden and too strong strains, which may break or damage the cable. Another problem with the known technique is that hydraulic control and feed systems are complicated, easily damaged and also expensive.
An object of this invention is to provide a method and an arrangement for cable winding on, and unwinding from, a reel in an electrically driven vehicle, by which method and arrangement drawbacks of the known solutions are avoided and cable winding and unwinding can be controlled as well as possible. A particular object of this invention is to eliminate the variations in cable tension caused by the large mass of the cable reel and its variation when the vehicle is accelerated or braked, to keep the cable tension as even as possible in spite of great variation in the cable reel, and to increase the service life of the cable from some hundreds of hours even up to some thousands of hours.
The method of the invention is characterized in that cable winding and unwinding, respectively, are controlled on the basis of the position of driving and/or steering means of the vehicle.
The arrangement of the invention is further characterized in that it comprises only one unwinding valve connected in series with the hydraulic motor, by which valve the counterpressure of the hydraulic fluid flowing through the hydraulic motor and thus the rotational resistance of the hydraulic motor can be regulated during cable unwinding from the reel, and one winding valve, respectively, by which the quantity of hydraulic fluid coming to the hydraulic motor can be regulated during cable winding. The arrangement also comprises control means connected to control the unwinding valve and the winding valve during cable unwinding and winding, respectively, and that at least part of the driving and steering means of the vehicle are connected to control the control means.
The essential idea of the invention is that cable winding on a reel or unwinding from the reel is controlled on the basis of the operation of the driving and steering means of the vehicle and by measuring the cable quantity on the cable reel, whereby a programmable logic can attend to the cable winding and unwinding on the basis of the properties of the vehicle, preferably by means of a table stored in the memory of the control logic. Then the cable winding and unwinding can be arranged in such a way that the cable is wound or unwound at the same speed as the vehicle moves including when it is accelerated and braked. This prevents the cable from being strained unnecessarily in any driving situation and eliminates at the same time the dragging of the cable when the vehicle is turning.